Role of PKA regulatory subunit R2B in murine and human adipocyte differentiation
Federica Ermetici1, Erika Peverelli1, Giovanna Mantovani1, Sabrina Corbetta2, Laura Avagliano1,3, Gaetano Bulfamante1,3, Paolo Beck-Peccoz1 & Anna Spada1
PKA regulatory subunit 2B (R2B) is the most expressed in mouse adipose tissue, where it plays an important role in regulating energy balance. We previously demonstrated that R2B is the most abundant R subunit in human adult subcutaneous and visceral adipose tissues. We further showed that R2B expression and PKA activation are reduced in adipose tissues from obese as compared to non-obese subjects. Normal adipose tissue development and increases in fat mass associated with obesity require the formation of mature adipocytes from preadipocytes or stromal progenitor cells and this process needs intracellular cAMP increases. Here, we investigated the role of R2B subunit in the differentiation of preadipocytes to mature adipocytes. R2B subunit was expressed at low levels in 3T3-L1 preadipocytes, which expressed high levels of the preadipocytes marker and cell fate determinant, Pref-1. A treatment with a mixture of methylisobutylxanthine, dexamethasone and insulin increased R2B expression levels 48 h after differentiation induction, when the expression of Pref-1 dramatically decreased. This pattern of R2B expression was evaluated in vivo in the adipocytes differentiation process during human fetal development. Immunostaining for PKA R2B, R2A and R1A showed that R2B protein was highly expressed in retroperitoneal mesenchymal cells from 14 and 20 weeks fetuses, as well as in the retroperitoneal adipocytes and subcutaneous adipose tissue from 37 weeks fetuses. On the contrary, R1A and R2A subunits were absent or very weakly expressed in all samples. Pref-1 colocalized with R2B in retroperitoneal mesenchymal cells from fetuses of early gestational ages, dramatically decreased at later gestational ages, while R2B expression levels increased, and it was absent in full term mature adipose tissue.
In conclusion, R2B is the PKA regulatory subunit mainly expressed in both preadipocytes and adipocytes during human fetal development. These preliminary data suggest that R2B might be involved in adipocyte differentiation and that it might be a target for future obesity treatment.